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Station X


Memories of Station X

The Rev. Alan Rogers was a Cryptanalyst at Station X, located at Bletchley Park during WW2. These two articles first appeared in the December 2000 and November 2002 editions of the 'Catswhisker', the newsletter of the South Dorset Radio Society and summarise the talks Alan gave us at our meetings.

Geoff, G0EVW - October 2002.

PART 1 - November 2000

The flag on the radiator of the staff Humber meant 'Very Important Person'. As the WREN brought the car to a halt outside the Ministry of Something Very Secret at St. Anne's Gate, London, out stepped Cpl Alan Rogers, not yet out of his teens, an attache case handcuffed to his wrist. He was shown to an impressive room where he waited and helped while some Even More Important People tried to make sense of a secret document.

Good start to a novel? No! But certainly it was a normal event in the extraordinary tale Alan told us of his time as a Cryptanalyst (=codebreaker) at Bletchley Park during the War.

The SDRS has (probably) never paid such rapt attention to a guest speaker. They were held enthralled as he explained how the German code FISH was eventually solved - while admitting that some aspects were never cracked.

He recalled being seconded to BP from Cambridge University where Prof. Adcock had recognised his mathematical talent. There were about 1,000 codebreakers, supported by 11,000 others, mainly women.

Alan showed how the FISH code worked: it was very, very complex and in various forms was used for many top secret German messages. A letter was never represented by the same code regularly. Its new assignation was determined by a series of wheels which clicked on, or didn't. Encoding and decoding could only be done with a 'key' or sequence of words. Deciphering was made easier by the mighty Colossus, the world's first programmable computer, a beast with 1,500 thermionic valves generating such heat as to melt solder connections. It filtered out rubbish from its attempts to make sense of codes and left the cryptanalysts something that might - just might - mean something. It looked for common associations of letters often occurring in the German language. The Germans themselves applied typical teutonic order to what should have been random events, their messages often ending with 'Heil Hitler' and never containing letters that represented themselves - so there were two clues that helped the codebreakers.

In the end, the 10 Colossuses (-i?) could help to decipher a message in 12 hours.

Like all the others, Alan only knew what he had to: they were forbidden from talking about their work. Regrettably, Alan's father and mother never lived to learn what he had done in the War.

What an extraordinary, engrossing talk! Thank you Alan.
John, M0BQO - December 2000

PART 2 - October 2002

At our October meeting we were privileged to have a return visit by the Rev. Alan Rogers who talked again about his days at Station X, the top-secret centre for deciphering enemy codes, located at Bletchley Park in Buckinghamshire during WW2. Back in November 2000 Alan had told us how he was recruited to work as a cryptanalyst and worked on the incredibly difficult task of breaking the very highest level of the German codes used between Hitler and his Generals, known as FISH. So called because the names of fish were given to the different communication routes.

Alan explained, in great detail and with the aid of diagrams how the Lorenz SZ40 series of machines worked and how much more complex they were than the Enigma machines. He told us that the Baudot Teleprinter Code (later known as the International Telecommunications Union number 2 alphabet) that the machine used was in fact an early binary system. Each character being represented by 5 data bits of either a Mark (1) or Space (0). We were very surprised to hear that experienced operators could actually decode the sound of the transmissions in the same way that most of can the Morse Code!

Incredibly the cypher system used was originally invented in America in 1918 by Gilbert Vernam and took advantage of the fact that in binary maths addition is the same as subtraction so that an identically set cypher machine at the receiving end of a link produced clear text when fed with the encyphered message.The Lorenz machine took Vernam's idea a stage further by adding another level of encryption. With the aid of more diagrams Alan then worked through some examples of FISH encryption and decryption while the very attentive audience did it's best to keep up. I am sure I was not alone in marvelling at how Alan, who worked entirely without notes during his lecture managed to recall all the detail. Even after almost 60 years he could still remember the Baudot Code. He made me feel very inadequate indeed!

The code-breakers at BP worked 24 hours a day in 8 hour shifts, handing on their work to the next group as they left. It was their proud boast that everything from the listening stations was decrypted the same day as it arrived. The pressure to keep up was immense and many fell ill from the stress and had breakdowns. Because of the very high security, treatment was at a special hospital provided for the Bletchley staff.

Alan finished his talk by briefly describing, yet again with the aid of diagrams, what he described as a 'simple' code used by the Romanian Siguranta, insisting that is was easy to break! He also mentioned the Soviet VENONA code, that because it used One Time Pads, (code sheets that were uniquely random and never reused) was almost unbreakable, with only one in about a thousand messages being read.

After thanking Alan for yet another enthralling talk, Neville, M5NEV presented him with a specially produced and inscribed edition of the late Ted Hall's 'The Suitcase Set' that he had produced for the occasion.

We were sent on our way with some homework to do and the promise that Alan would report outstanding success at same to his friend at GCHQ who was always looking for new recruits!
Geoff, G0EVW - October 2002


Station X - The Codebreakers of Bletchley Park by Michael Smith.
A Channel 4 book produced to accompany the TV series.
ISBN 0 7522 2189 2

Information Sheets provided by the Rev. Alan Rogers at the meeting.